The invention relates to the field of very-high-density memory device that utilizes a scintillating medium for data storage.
With the development of the internet, the desire for video-on-demand services, and increases in high-volume-data applications, the demand for high-density memory will continue to grow. Currently, there are two prevalent types of high-density data storage media. One is based on magnetic storage and the other is termed optical-data storage. For commercial magnetic-storage media, data-storage densities of about 2 billion bits per square centimeter (2 Gb/cm2) have been achieved. Data storage densities of about 100 Mb/cm2 have been achieved for commercial optical data storage. It is desirable to obtain even higher memory-storage densities.
Both magnetic-storage and optical-storage techniques incur significant technical difficulties as the data-storage density is increased. For magnetic storage, increasing densities imply a smaller size for the individual magnetic bit, and this reduction in size leads to a decreasing magnetic field. The data-reading head must then be moved closer to the disk to detect the bit. Presently, the magnetic reading head rides on a cushion of air and floats much less than 1 micron above the disk surface. As the bits are placed closer to each other, they are likely to interact and spontaneously flip the magnetic field from bit to bit, ruining the stored data.
Optical-data storage suffers from a similar problem of data readability. For CD-ROM, the bit size cannot be made significantly smaller than the probing size of the focused optical field at the substrate. This probe size is on the order of 1 micron for laser diodes and inexpensive optical lenses. Novel near-field optical reading schemes have been proposed (see Martin et al., Appl. Phys. Lett., Vol. 7 (1997)), but the reading head must be brought to within 0.01 microns from the surface to detect the bit. Any particles on the storage-medium""s surface could irreversibly damage the reading head for both optical-and magnetic-storage schemes. It is desirable to locate the data-reading head several millimeters from the storage-medium""s surface.
A related problem for magnetic- and optical-data-storage devices pertains to the quality of the signal derived from the stored data, i.e., how well can a xe2x80x9clowxe2x80x9d data bit be distinguished from a xe2x80x9chighxe2x80x9d data bit. As the bit size decreases, the signal level from the data bit decreases while system noise remains unchanged. The resulting noisy signals for magnetic- and optical-data-storage devices are likely to cause data read-out errors.
Another problem that will be incurred by very-high-density magnetic and optical-data-storage devices is an inability to follow the data tracks precisely on the data-storage medium. As the data tracks are packed closer together, the reading head must be able to navigate directly along the data track, which may be deviated. It is likely that the massive reading heads for magnetic- and optical-data-storage devices will xe2x80x9cjumpxe2x80x9d data tracks, since they cannot be deflected easily at high speeds to follow the data path. It is desirable to provide a means for precisely following the data tracks at high speeds or read-out rates.
The invention provides a system for storing data on a scintillating medium and reading the data with an electron beam, which impinges on the scintillating medium through vias that define the stored data, and a sensitive photodetector, which is located near the scintillating medium. The system is also capable of following the data tracks in the scintillating medium where the medium may be in the shape of a rectangle, a circular disk, or a cylinder. The system also is capable of patterning data tracks or stored data in the storage medium.
In one embodiment, a single electron source is used to probe a spinning, scintillating data-storage disk, and a single photodetector is used to detect the scintillation signal, corresponding to the stored data in the storage disk. In another embodiment, multiple electron beams and photodetectors are used to read the data from the scintillating data-storage medium in parallel.
In an alternative embodiment, an electron beam is used to write the data to the scintillating medium by locally damaging the scintillating medium. In another embodiment, the data may be patterned onto the scintillating medium using deep-ultraviolet contact photolithography and embedded attenuating-phase-shift masks. In yet another embodiment, the data tracks may be patterned onto the scintillating medium using a novel mode of interferometric lithography. The technique for patterning the data or data tracks on the scintillating medium may be used for patterning very-high-density magnetic-data-storage and optical-data-storage media.
The invention provides a system for obtaining data-storage densities greater than 20 billion bits per square centimeter (20 Gb/cm{circumflex over ( )}2). There is a fundamental amplification of the signal in the scintillating data-storage medium, and the contrast (on-to-off ratio) of the data signal can be infinite in principal. Additionally, the signal level remains constant as the bit size decreases for the very-high-density memory device of the invention.